Conductive materials are used in myriad electronics applications as a finish contact surface. Gold, for example without limitation, has been traditionally valued in the electronics industry for its excellent resistance to environmental oxidation, low resistivity, and as a consequence is frequently used in finish contact surfaces. For example, in connector applications, a connector substrate material, such as copper, can be coated with a layer of gold. Depositing gold directly over the substrate, however, is detrimental to the contact resistance of the connector. Copper and gold, for example, undergo solid state inter-diffusion even at room temperature; the copper diffuses through the gold layer causing the gold to tarnish and corrode. Additionally, the electrical resistivity of the resulting alloy material is much higher than the resistivity of either element alone. In practice, a barrier layer, such as, for example without limitation, a layer comprising nickel, is typically deposited over the substrate surface prior to the conductive layer deposition. Some metals, such as gold, are softer than the barrier and substrate layers (e.g., nickel and copper), and as such the barrier layer serves as a backing to the finish contact layer to provide added hardness.
In connector applications in which insertion, particularly repeated insertions, is a necessity, contact surface loss or wear due to fretting or galling is problematic because loss of material on the contacting surface results in undesirable higher contact resistance. Traditionally, the thickness of the contact surface is increased as the expected number of insertions increases. For example, connectors requiring few insertions may be coated with about 0.2 to about 0.5 microns of contact surface material, while those requiring larger number of insertions may be coated with about 1.5 microns or more of gold. FIG. 1 illustrates an exemplary prior art connector 10 comprising substrate layer 12, barrier layer 14, and contact surface layer 16. Connector 10 represents any one of connector structures (device structures) 10.1, 10.2 of FIG. 14; one of structures 10.1 and 10.2 is insertable into the other. Some conductive metals, such as gold, price at over $1,200/oz. It would be beneficial to have a lower cost contact structure, one whose contact layer thickness is either independent of the number of expected insertions, or is reduced relative to the thickness in traditional connectors.